1. Field of the Invention
The present invention relates to a color display apparatus in which a light beam is intensity-modulated with a so-called color video format signal, that is, a color video signal including a composite synchronizing signal composed of vertical and horizontal signals, etc., and is caused to perform two-dimensional scanning. The scanning occurs on a screen in synchronization with the composite synchronizing signal to reproduce a picture.
2. Description of the Relates Art
Referring to FIG. 7, an example of the conventional color display apparatus will be described.
In FIG. 7, a helium neon laser generator 1 generates red laser light (having a wavelength of 633 nm), an argon ion laser generator 2 generates green laser light (having a wavelength of 515 nm), and a helium cadmium laser generator 3 generates blue laser light (having a wavelength of 441 nm). The laser light of the three primary colors is supplied to light modulators 4, 5 and 6. Light modulators 4, 5 and 6 generate R, G and B signals that each carry color video information as modulating signals.
The intensity of the red laser light is modulated by the light modulator 4 in accordance with the level of the R signal. The direction of light is changed by a reflection mirror 7 so as to enter a reflection mirror 10 through dichroic mirrors 8 and 9. The intensity of the green laser light is modulated by the light modulator 5 in accordance with the level of the G signal. The direction of light is changed by the dichroic mirror 8 so as to enter the reflection mirror 10 through the dichroic mirror 9. Finally, the intensity of the blue laser light is modulated by the light modulator 6 in accordance with the level of the B signal. The direction of the light is changed by the dichroic mirror 9 so as to enter the reflection mirror 10.
A single light beam comprising the three primary colors, mixed by the dichroic mirrors 8 and 9, is emitted from the reflection mirror 10. This single light beam is deflected by a reflection mirror 11 of a galvanometer that is arranged to swing in synchronization with a vertical synchronizing signal of a video signal. The light beam is then passed through a pair of relay lenses 12a and 12b and is further deflected by a rotary polyface mirror 13. Rotary polyface mirror 13 is arranged to rotate in synchronization with a horizontal synchronizing signal of the video signal.
The direction of the light beam deflected by the rotary polyface mirror 13 is changed by a reflection mirror 14 to reflect the beam on a screen 15, and thereby scan the screen. The spot diameter of the light beam is adjusted by a lens of an optical system (not shown).
In the display apparatus described above, the intensity of three color laser beams, red, green, and blue, are modulated by light modulators with color television three-primary-color signals. The three beams are mixed into one light beam by dichroic mirrors, and projected by mechanical light deflectors onto a two-dimensional scanning screen. This arrangement produces a color television display apparatus having high resolution and high chromatic quality. The relay lenses 12a and 12b are used to make the rotary polyface mirror 13 small-sized.
FIG. 8 shows a control system of the color display apparatus, in which a data processor 20 is arranged to separate a video signal from a color video format signal supplied thereto, to demodulate the separated video signal into R, G and B signals. The data processor 20 then supplies the demodulated R, G and B signals to a driver 21 in accordance with a command supplied from a controller 22. The driver 21 amplifies the R, G and B signals and supplies the amplified signals to the light modulators 4, 5 and 6, respectively.
The data processor 20 also separates horizontal and vertical synchronizing signals from the color video format signal and supplies the separated synchronizing signals to the controller 22. The controller 22 is constituted by a micro-processor, PLL circuits for horizontal and vertical deflection, and so on. The vertical deflection PLL circuit is arranged to generate a driving signal in synchronism with the vertical synchronizing signal supplied thereto. The vertical deflection PLL circuit also supplies the driving signal to a galvanometer 23 to cause the galvanometer 23 to swing the mirror 11. Thus, the reflection mirror 11 reciprocates with a vertical period synchronous with the vertical synchronizing signal. The rotational position of the reflection mirror 11 is detected by an encoder 24 interlocked with the galvanometer 23. The detection output of the encoder 24 is fed back to the vertical deflection PLL circuit of the controller 22 and phase-compared with the vertical synchronizing signal. Feedback control is thus performed to establish synchronization between the vertical synchronizing signal and vertical scanning.
The horizontal deflection PLL circuit is arranged to generate a driving signal synchronized with the supplied vertical synchronizing signal and supplies the driving signal to a motor 25 so as to rotate the rotary polyface mirror 13. The rotational position of the rotary polyface mirror 13 is detected by an encoder 26 interlocked with the motor 25. The detection output of the encoder 26 is fed back to the horizontal PLL circuit of the controller 22 and phase-compared with the horizontal synchronizing signal so that feedback control is performed. This feedback control establishes synchronization between the horizontal synchronizing signal and the horizontal scanning. The controller 22 generates a supply command to the data processor 20 in agreement with the start timing of the horizontal scanning of the light beam.
Thus, the scanning on the screen surface by the light beam is deflected two-dimensionally by the mechanical light deflectors, and the intensity and color change of the light beam are synchronized with each other to project a picture on the screen.
However, such a color display apparatus has the disadvantage of being expensive because it requires three light-beam generators for generating three light beams of three primary colors and an optical system for mixing those three primary colors.